A route metric specifies the cost of a route to a specified destination address.
The following factors often affect the route metric:
Path length
The path length is the most common factor affecting the route metric. Link-state routing protocols allow you to assign a link cost for each link to identify the path length of a link. In this case, the path length is the sum of link costs of all the links that packets pass through. Distance-vector routing protocols use the hop count to identify the path length. The hop count is the number of devices that packets pass through from the source to the destination. For example, the hop count from a router to its directly connected network is 0, and the hop count from a router to a network that can be reached through another router is 1. The rest can be deduced in the same manner.
Network bandwidth
The network bandwidth is the transmission capability of a link. For example, a 10-Gigabit link has a higher transmission capability than a 1-Gigabit link. Although bandwidth defines the maximum transmission rate of a link, routes over high-bandwidth links are not necessarily better than routes over low-bandwidth links. For example, when a high-bandwidth link is congested, forwarding packets over this link will require more time.
Load
The load is the degree to which a network resource is busy. You can calculate the load by calculating the CPU usage and packets processed per second. Monitoring the CPU usage and packets processed per second continually helps learn about network usage.
Communication cost
The communication cost measures the operating cost of a route over a link. The communication cost is another important indicator, especially if you do not care about network performance but the operating expenditure.